This application is related to, and claims priority to, Japanese Application No. JP 2001-337832 filed Nov. 2, 2001, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a photoconductor for electrophotography (hereinafter also referred to simply as xe2x80x9cphotoconductorxe2x80x9d) and a manufacturing method thereof. The invention more particularly relates to a layered or a single layer photoconductor having a photosensitive layer containing an organic material, and a manufacturing method thereof. The photoconductor of the invention is used in devices such as an electrophotographic printer, an electrophotographic copying machine, etc.
2. Description of the Related Art
A photoconductor has a structure in which a photosensitive layer having photoconductivity is layered on a conductive substrate. Prevailing photoconductors may be classified as single layer and layered. The single layer photoconductor has a single photoconductive layer with combined functions of charge generation and charge transport. The layered photoconductor has photoconductive layers functionally separated into a layer contributing charge generation and a layer contributing surface charge holding and charge transport. Further, in recent years, a photoconductor using organic material has been brought into practical use because of advantages of having excellent thermal stability and film formability. In such photoconductors, however, it is difficult to form mechanically stable photosensitive layers with only functional material performing charge generation and charge transport. Therefore, photosensitive layers are normally formed with resin binders and used together to form the photoconductors.
A photoconductor that has recently become mainstream is the layered photoconductor in which a charge generation layer including a charge generation material, and a charge transport layer including a charge transport material, are used. In particular, in the negative charging photoconductor, the charge generation layer is formed with organic pigments vapor deposited or dispersed in resin binder. Also, the charge transport layer includes particles of an organic low-molecular-weight compound having charge transporting properties that are dispersed in resin binder as charge transport material. In addition, in a positively charged photoconductor, a single photosensitive layer is used with charge generation material and charge generation material dispersed in resin binder.
Furthermore, to enhance the quality of printed images, an undercoat layer is generally provided between the conductive substrate and the charge generation layer or the photosensitive layer. In particular, when a photoconductor is applied to a Carson process electrophotographic device, the undercoat layer is provided under the charge generation layer or the photosensitive layer to prevent defects such as black spots and white spots from being produced on a printed image.
The undercoat layer is formed of materials such as casein, polyamide resin, polyvinyl butyral resin, polyethylene, polypropylene, polystyrene, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, polyvinyl formal resin, polyurethane resin, epoxy resin, phenoxy resin, polyester resin, melamine resin, and silicone resin.
To prevent interference by laser exposure light and provide conductivity for the undercoat layer, dispersed in a resin of the undercoat layer are metal oxide fine particles, resin particles insoluble in a solvent of coating liquid for the undercoat layer (hereinafter simply referred to as xe2x80x9ccoating liquidxe2x80x9d), or particles for which those resin particles are surface treated.
The metal oxide fine particle, however, has a larger specific gravity compared with that of the resin binder used in the undercoat layer. Thus, the particles are easily sedimented or separated in the coating liquid for the undercoat layer. This tends to cause nonuniformity in characteristics and nonuniformity in external appearance of the undercoat layer when the undercoat layer is formed. Therefore, for obtaining uniformity of the coating liquid for the undercoat layer, dispersion stability in the coating liquid is required for the metal oxide fine particles.
Several methods have been proposed to deal with this problem. Such methods include, for example, a dip coating method for an electrophotographic photoconductor using a solvent having specified boiling point and viscosity (see Japanese patent application JP-A-4-352159); a manufacturing method of an electrophotographic photoconductor using metal oxide fine particles surface treated by a specified coupling agent, a binder resin, and a coating liquid for an undercoating containing a specified organic solvent (see Japanese patent application JP-A-10-148959); and a coating liquid for manufacturing an electrophotographic photoconductor using a combination of a specific binder resin, titanium oxide particles, and a solvent (see Japanese patent application JP-A-2000-258941). However, none of these methods sufficiently satisfies the currently required level of dispersion stability of metal oxide fine particles. Thus, a photoconductor has been desired that provides excellent uniformity in a coating liquid for an undercoat layer without producing a poor image due to the coating liquid.
Accordingly, it is an object of the present invention to achieve a uniform undercoat layer by improving dispersion stability of metal oxide fine particles in a coating liquid for the undercoat layer of a photoconductor for electrophotography, and a manufacturing method thereof. It is also an object of the present invention to provide a photoconductor for electrophotography with uniform electrophotographic characteristics, in particular, with uniform image characteristics and external appearance characteristics.
Additional objects and advantages of the invention will be set forth in part in the description that follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
Dispersion stability of the coating liquid can be improved by bringing a boiling point and a viscosity of an organic solvent used for the coating liquid for the undercoat layer within a specified range. Such an organic solvent can eliminate nonuniformity in photosensitive characteristics and external appearance characteristics of the obtained photoconductor to obtain an excellent photoconductor having uniform characteristics.
To achieve the above and other objects according to an embodiment of the present invention, there is provided a photoconductor having a conductive substrate, an undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the undercoat layer. The undercoat layer contains metallic oxide fine particles and is formed by applying a coating liquid for the undercoat layer onto the conductive substrate. The coating liquid for the undercoat layer contains an organic solvent having a boiling point at 1xc3x97105 Pa of about 160xc2x0 C. or less and a viscosity at 20xc2x0 C. of about 3.0 mPa.s or more.
The photosensitive layer can be either a layered type, formed with a charge generation layer and a charge transport layer, or a single layer type, which is formed in a single layer and contains a charge generation material and a charge transport material.
The organic solvent is an alcohol solvent having 4 or more carbon atoms or, alternatively, an alcohol solvent having 4 or more carbon atoms with a branch structure.
To achieve the above and other objects according to another aspect of the present invention, there is provided a method of manufacturing a photoconductor including applying a coating liquid onto a conductive substrate to form an undercoat layer. The coating liquid contains metallic oxide fine particles and an organic solvent, and the organic solvent has a boiling point at 1xc3x97105 Pa of about 160xc2x0 C. or less and a viscosity at 20xc2x0 C. of about 3.0 mPa.s or more.